The present application is related to co-pending U.S. patent application Ser. No. 09/380,247, entitled xe2x80x9cM-TYPE MICROWAVE DEVICExe2x80x9d, filed Aug. 30, 1999 and U.S. patent application Ser. No. 09/380,248, entitled xe2x80x9cMAGNETRONxe2x80x9d, filed Aug. 30, 1999, both of which are hereby incorporated by reference into this specification in their entirety.
The present invention relates generally to the field of electronics, and more particularly, to field emitters used in M-type microwave devices.
Well known are microwave devices such as that disclosed in Russian Patent No. 2007777, which have field emission cathodes having interfaces for the purpose of preventing of thermal diffusion of corrosively active materials. These interfaces are shaped as discs made of material which are placed on both sides of a field emitter operating film made of foil having a thickness of 0.5 to 5xcexc. The discs have a greater thickness than the foil. One of the drawbacks of Russian Patent ""777 is the inability to control the thickness of the foil used as the field emitter. It is essentially impossible to assemble such an emitter at a definite thickness of the foil. Besides, non-uniform thermal contact between the operating film and protective discs along the circumference does not allow heat to be effectively carried off from the field emitter during its operation. This may lead to damage of the field emitter because of overheating and melting.
Other types of microwave devices are also known such as that disclosed in Russian Patent No. 1780444 where a two-layer structure, consisting of the field emitter operating film applied on a foil substrate, is used as a field emitter. The basic drawback of the Russian Patent ""444 is that one side of the operating film is not protected from mechanical and diffusion processes both during the assembly and the operation of the device. Such exposure reduces the film""s mechanical strength and reliability as well as the lifetime of the whole field emitter.
These deficiencies in the prior art are addressed by the present invention.
The present invention relates to electronics and particularly to field emitters used in M-type microwave devices. The design of a multi-layer field emitter is proposed which has at least one operating film and supporting films, providing mechanical strength and preventing penetration of corrosive materials into the operating film at high operating temperatures. The supporting films could be produced from the same material or material with linear expansion coefficients equal or close to that of the operating film material. Built-in mechanical stress can cause not only deformation but also breakage of the film when exposed to a wide range of temperatures. In the inventive structure thermal stresses in the operating film during an emission from its surface are lower due to good thermal contact with supporting films.
General advantages of the field emitter of the present invention compared to the prior art is that the present invention is mechanically stronger and more reliable which makes the cathode assembly easier. The present invention has a minimum of mechanical tensions which provides safe operation in a wide temperature range. The present invention provides operation while in contact with corrosively active materials under high temperature.
The operating film of a field emitter in accordance with the present invention could be as thin as a few angstroms which permits this design to be used in a variety of devices. Additionally, the supporting films have a direct contact with the operating film, thus carrying off heat effectively from the emitter during its operation.
Production of the field emitters may be based on well developed technological processes currently used in mass production of thin film circuits and allowing the production of inexpensive mono- and multi-emitter systems.
In accordance with an aspect of the present invention, a method of manufacturing a field emitter for a magnetron is described. The method includes depositing three layers of film on a substrate. At least one protective mask is placed on an uppermost layer of the three layers. The three layers not protected by the at least one protective mask are first removed. Horizontal and vertical portions of the first and third layers of the remaining three layers are exposed. Oopposite edges of the first and third layers are removed. The at least one protective mask and the substrate are removed leaving at least one field emitter.
In accordance with another aspect of the present invention, a field emitter for a magnetron is described. The field emitter includes a central operating layer having a first edge and a second edge and a first surface and a second surface. At least one first support layer is on the first surface. The first edge and the second edge extend beyond the first support layer and the second support layer.
In accordance with another aspect of the present invention, a method of manufacturing a field emitter for a magnetron is described. The method includes depositing three layers of film on a substrate. At least one protective mask is placed on an uppermost layer of the three layers. Portions of the three layers not protected by the at least one protective mask are removed to form a plurality of stacks of layers of film and to expose an upper surface of the substrate therebetween. A fourth layer of film is deposited onto an upper surface of the at least one protective mask and on the exposed upper surface of the substrate. The layers of film and protective mask are removed above the partially etched layer. A portion on the second layer of film is partially removed to expose a portion of the upper surface of the second layer. A fifth layer of film is deposited on the remaining partially etched layer, the portions of the upper surface of the second layer, and an upper surface of the additional layer; removing the partially etched layer and the layer of film above the partially etched layer; depositing a sixth layer on the upper surface of the first layer and on a portion of the fourth layer; depositing a seventh layer of film on an upper surface of the sixth layer of film; and removing all layers except for the fourth layer, the fifth layer and the seventh layer.
Still other aspects of the present invention will become readily apparent to those skilled in the art from the following detailed description, wherein the preferred embodiments of the invention are shown and described, simply by way of illustration of the best mode contemplated of carrying out the invention. As will be realized, the invention is capable of other and different embodiments, and its several details are capable of modifications in various obvious respects, all without departing from the invention. Accordingly, the drawings and description thereof are to be regarded as illustrative in nature, and not as restrictive.